Radio frequency module

ABSTRACT

In a compact radio frequency module, a first chip forms a heater element and a second chip forms a device whose operating characteristics vary with temperature change or whose maximum operating temperature is lower than the maximum operating temperature of the first chip. A multilayer substrate has a plurality of dielectric layers and a plurality of conductor layers and mechanically supports the firs chip and the second chip with some of the conductor layers electrically connected with these chips. The module can conduct the heat generated by the first chip throughout the module; guide the heat generated by the first chip from the module&#39;s top face side to its bottom face side; and interrupt the heat conduction from the first conductor pattern on which the first chip is placed to the second conductor pattern on which the second chip is placed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications andparticularly to radio frequency components for use in mobilecommunication terminals such as mobile phones and wireless communicationterminals such as wireless LAN, which feature increased function, highintegration, reduced size and low price.

2. Description of the Related Art

With the growing tendency towards more compact wireless communicationterminals, there is demand for radio frequency components for wirelesscommunication terminals that fit into a smaller packaging area.Conventionally, circuit of radio frequency parts have been divided intoseveral blocks by function and the blocks have been manufacturedseparately as modules while efforts have been made to improvereliability, reduce size and increase integration for each module. Forexample, methods of heat dissipation in power amplifier (hereinafterreferred to as PA) modules including power amplifiers as heater elementsare disclosed in JP-A No.27570/1997 and JP-A No. 147349/1995.

In recent years, JP-A No.8584/1997 and JP-A No. 266546/1999 disclosetechniques which produce more compact radio frequency components withhigher integration in function by combining modules which would beseparately manufactured in the former methods.

PA requires a heat dissipation structure because it consumes muchelectric power and generates heat. For this reason, various PA modulestructures for effective heat dissipation are disclosed: one example isa multilayer substrate which has, on its surface layer, an electricallyisolated metallized layer or a metallized layer connected to a groundinglayer (JP-A No.147349/1995) and another example concerns a structure ofa substrate in which the almost whole surface of the ceramic substrateis covered with a metal layer and through holes for heat dissipation areuniformly distributed almost all over the substrate (JP-A No.27570/1997).

However, these conventional techniques have the following drawback: in amodule which integrates a power amplifier and a device whose operatingcharacteristics vary with rise in temperature, namely a device havingsensitive temperature dependence of characteristics, on a substrate, theinfluence of the heat generated by the PA on the device having sensitivetemperature dependence of characteristics is not taken intoconsideration, or though it is taken into consideration to mount a PAand a device having sensitive temperature dependence of characteristicstogether in a module, attention is not paid to the fact that part of theheat is conducted in the module substrate and then to the above-saiddevice having sensitive temperature dependence of characteristics.

Therefore, in the conventional techniques, when a device havingsensitive temperature dependence of characteristics is mounted togetherwith a power amplifier on a substrate, the fair distance between boththe devices was needed to avoid the influence of the heat generated bythe power amplifier. Furthermore, a deterioration in electricalcharacteristics which is caused by change in characteristics withtemperature rise has been unavoidable. For this reason, it has beenimpossible to produce a compact, high performance radio frequency modulein the form of both a power amplifier, which generates heat, and adevice having sensitive temperature dependence of characteristics aremounted together.

SUMMARY OF THE INVENTION

The present invention introduces a new concept of suppressingtemperature rise in the part of a substrate where the above-mentioneddevice having sensitive temperature dependence of characteristics isplaced for a radio frequency module where a power amplifier and thedevice having sensitive temperature dependence of characteristics areintegrated, thereby solving the above problem and realizing a compact,high-performance radio frequency module.

The present invention focuses the structure of a radio frequency modulewhich solves the above problem and particularly the arrangement ofconductor layers.

According to one aspect of the present invention, a radio frequencymodule comprises at least: a first chip forming a heater element; asecond chip forming a device whose operating characteristics vary withtemperature change or whose maximum operating temperature is lower thanthe maximum operating temperature of the first chip; and a multilayersubstrate which is comprised of a plurality of dielectric layers and aplurality of conductor layers and mechanically supports the first chipand the second chip with some of the conductor layers electricallyconnected with these chips, wherein the first chip is located on aconductor layer provided on the top face of the multilayer substrate oron a first conductor pattern made on a conductor layer inside a cavitymade in the multilayer substrate; the second chip is located on aconductor layer provided on the top face of the multilayer substrate oron a second conductor pattern made on a conductor layer inside a cavitymade in the multilayer substrate; and when the multilayer substrate isfixed on another substrate, it is fixed with its bottom face in contactwith the other substrate, and the module has at least one of thefollowing means: means for conducting the heat generated by the firstchip throughout the module; means for guiding the heat generated by thefirst chip from the module's top face to its bottom face; and means forinterrupting heat conduction from the first conductor pattern to thesecond conductor pattern.

According to another aspect of the invention, a radio frequency modulecomprises at least: a first chip forming a heater element; a second chipforming a device whose operating characteristics vary with temperaturechange or whose maximum operating temperature is lower than the maximumoperating temperature of the first chip; and a multilayer substratewhich is comprised of a plurality of dielectric layers and a pluralityof conductor layers and mechanically supports the first chip and thesecond chip with some of the conductor layers electrically connectedwith these chips, wherein the first chip is located on a conductor layerprovided on the top face of the multilayer substrate or on a firstconductor pattern made on a conductor layer inside a cavity made in themultilayer substrate; the second chip is located on a conductor layerprovided on the top face of the multilayer substrate or on a secondconductor pattern made on a conductor layer inside a cavity made in themultilayer substrate; and when the multilayer substrate is fixed onanother substrate, it is fixed with its bottom face in contact with theother substrate and the first conductor pattern and another conductorpattern electrically connected with the first conductor pattern areisolated from the second conductor pattern and another conductor patternelectrically connected with the second conductor pattern at theconductor layer in which the second conductor pattern is formed andconductor layers closer to the top face of the multilayer substrate thanthe conductor layer in which the second conductor pattern is formed.

According to a further aspect of the invention, the first conductorpattern and another conductor pattern electrically connected with thefirst conductor pattern are isolated from the second conductor patternand another conductor pattern electrically connected with the secondconductor pattern at the conductor layer in which the second conductorpattern is formed and conductor layers closer to the top face of themultilayer substrate than the conductor layer in which the secondconductor pattern is formed and the former conductor patterns areconnected with the latter ones at least at one of the conductor layerslocated closer to the bottom face of the multilayer substrate than theconductor layer in which the second conductor pattern is formed.

According to a further aspect of the invention, a radio frequency modulecomprises a first chip; a second chip whose heat value per unit time maybe smaller than that of the first chip; and a multilayer substratecomprised of a plurality of conductor layers and a plurality ofdielectric layers, wherein the first chip and the second chip areelectrically connected with any of the conductor layers, and there are afirst structure for conducting the heat generated by the first chiphorizontally in the module and a second structure for conducting theheat vertically in the module.

A conductor layer may be used for the first structure. The conductorlayer can conduct the heat generated by the first chip horizontally.When the conductor layer extends to the substrate's outer edge area, itrealize easier heat conduction in a substrate. One approach tocontrolling the heat conductivity of the conductor layer is to cut offpatterns in the conductor layer. To this end, part of the conductorlayer may be removed or a groove may be made.

The first chip, for example a power amplifier, does not always generateheat but turns on and off periodically in some cases. The primary objectof the invention is to prevent the second chip from being affected bythe heat generated by the first chip which is operating.

According to a further aspect of the invention, as a method forpreventing heat conduction from the first chip to the second chip, aheat isolation zone which crosses the line connecting the first chip andthe second chip is specified on the main surface of the multilayersubstrate and the conductor layer area corresponding to the projectionfrom the heat isolation zone is removed or a groove is made in the areacorresponding to the projection from the heat isolation zone. Theconductor layer area corresponding to the projection from the heatisolation zone may be removed in all the conductor layers or in a singleconductor layer. Also, the whole area corresponding to the projection orpart of the area may be removed.

One example of the second structure is a via hole.

To put the first chip and the second chip at the different conductorlayer each other is effective to reduce the thermal effect to the secondchip, because the distance between the first chip and the second chipbecomes longer than that in case of mounting them on the same layer.

According to the present invention, even when a first device which has apower amplifying function and a second device which has sensitivetemperature dependence of characteristics such as a surface acousticwave device (hereinafter referred to as a “SAW” device) are integratedon a substrate, the temperature rise of the area in which the seconddevice is placed can be suppressed and its thermal interference with thefirst device can be reduced so that it is possible to provide a compactradio frequency module with higher integration in function which allowsthe first device and the second device to operate normally and stably.

The use of a radio frequency module according to the present inventionenables to realize of a more compact wireless communication terminal orif the size of a wireless communication terminal is fixed, it offersmore space for new additional functions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more particularly described with reference to theaccompanying drawings, in which:

FIG. 1 is a sectional view showing a first embodiment of the presentinvention;

FIG. 2 is a sectional view showing a second embodiment of the presentinvention;

FIG. 3A is a top view showing a conductor pattern on a conductor layer 5a according to the second embodiment of the present invention and FIG.3B is a top view showing a conductor pattern on a conductor layer 5 baccording to the second embodiment of the present invention;

FIG. 4A is a top view showing a conductor pattern on a conductor layer 5c according to the second embodiment of the present invention and FIG.4B is a top view showing a conductor pattern on a conductor layer 5 daccording to the second embodiment of the present invention.

FIG. 5A is a top view showing a conductor pattern on a conductor layer 5e according to the second embodiment of the present invention and FIG.5B is a top view showing a conductor pattern on a conductor layer 5 faccording to the second embodiment of the present invention;

FIG. 6 is a sectional view showing a third embodiment of the presentinvention;

FIG. 7 is a sectional view showing a fourth embodiment of the presentinvention;

FIG. 8 is a sectional view showing a fifth embodiment of the presentinvention;

FIG. 9 is a top view showing a conductor layer pattern according to thefifth embodiment of the present invention;

FIG. 10 is a sectional view showing a sixth embodiment of the presentinvention;

FIG. 11 is a sectional view showing a variation of the sixth embodimentof the present invention;

FIG. 12 is a perspective view showing a seventh embodiment of thepresent invention;

FIG. 13 is a perspective view showing an eighth embodiment of thepresent invention;

FIG. 14 is a sectional view showing a ninth embodiment of the presentinvention;

FIG. 15 is a perspective view showing a tenth embodiment of the presentinvention;

FIG. 16 is a sectional view showing the tenth embodiment of the presentinvention; and

FIG. 17 is another sectional view showing the tenth embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, preferred embodiments of the present invention will be describedin detail referring to the accompanying drawings. In the figures whichillustrate the embodiments, components which have the same functions aredesignated by the same reference numerals and components which are onceexplained will not be explained again.

FIG. 1 is a sectional view showing a radio frequency module according toa first embodiment of the present invention. The first embodiment is aradio frequency module in which a power amplifier 1 and a SAW device 2 () are mounted on a ceramic multilayer substrate 3. The SAW device 2 inthis embodiment has a function as a transmitting filter. The multilayersubstrate 3 is composed of six dielectric layers 4 a, 4 b, 4 c, 4 d, 4e, 4 f and seven conductor layers 5 a, 5 b, 5 c, 5 d, 5 e, 5 f, 5 g.According to the first embodiment, the power amplifier 1 is mounted bysilver paste or solder on a conductor pattern 10 formed on the conductorlayer 5 a. The SAW device 2 is mounted by silver paste or solder on aconductor pattern 13 formed on the conductor layer 5 e inside a cavity 6made by partially removing the dielectric layers 4 a to 4 d. Theconductor pattern on the surface of each device and the relevantconductor layer of the multilayer substrate are connected by bondingwires 7. The cavity, in which the SAW device 2 is located, ishermetically sealed by a cover 40. With a passive device 8 and the likeon the top face of the multilayer substrate, the substrate top iscovered by a lid 50.

In this embodiment, the multilayer substrate 3 has two areas: a firstarea 100 and a second area 200. The first area 100 includes the poweramplifier 1, the passive device 8 for its operation, a wiring pattern101 which connects them, and a conductor pattern 102 which serves as theground for the power amplifier 1; the second area 200 includes the SAWdevice 2 and a passive device 80 for its operation, a wiring pattern 201which connects them and a conductor pattern 202 which serves as theground for the SAW device 2.

The heat generated by the power amplifier 1 is conducted partially fromthe module surface and partially through the conductor pattern 10holding the power amplifier 1, then through conductor layers anddielectric layers or via holes 11 down to the bottom face 12 of themodule while being conducted horizontally and vertically. From thebottom face 12, the heat goes, for example, through a motherboard (notshown) on which the module is mounted, before being forced out of themodule (for example, dissipated into the air).

In the present invention, the SAW device 2, which has sensitivetemperature dependence of characteristics, and the power amplifier 2 areintegrated on the same multilayer substrate 3 so it is necessary tominimize temperature rise of the conductor pattern 13 holding the SAWdevice 2 in order to prevent or reduce the possibility of deteriorationin the SAW device 2.

For this purpose, preferably the module should have either of thefollowing structures or a combination of them: one structure is suchthat the heat is conducted throughout the module to reduce rise in theoverall temperature of the module; another structure is such that theheat can easily emanate from the conductor pattern 10 holding the poweramplifier 1 or from the conductor pattern 13 holding the SAW device; anda further structure is such that the heat from the power amplifier 1 ishardly transfered to the conductor pattern holding the SAW device 2.

In the first embodiment of the present invention, in order to facilitateheat conduction inside the module, as many conductors as possible areprovided in each of the first area 100 and the second area 200. In thefirst embodiment there is an area 300 where conductors are not connectedbetween the area 100 and the area 200 at the following conductor layers;conductor layers between the conducter layer in which the conductorpattern 13 is formed and the conductor layer in which the conductorpattern 10 is formed, namely conductor layer 5 a, 5 b, 5 c, 5 d and 5 e.Therefore, as the heat conducted from the conductor pattern 10 passesmainly through conductors or via holes 11 and enters the first area 100,the heat conductivity becomes low in the area 300 and the heat is hardlyconducted into the second area 200. As a result, the amount of heatwhich is conducted into the second area 200 decreases. Also in thesecond area 200, as many conductors as possible are provided in order toconduct the incoming heat throughout the second area 200. Therefore, theamount of heat which is conducted to the conductor pattern 13 holdingthe SAW device 2 decreases so that the temperature rise of the conductorpattern 13 can be suppressed, resulting in a reduction in thetemperature rise of the SAW device 2.

Consequently, even when the power amplifier 1 and SAW device 2 areintegrated into one module, the SAW device 2 can operate with stability.

Next, a second embodiment of the present invention is describedreferring to FIG. 2. FIG. 2 is a sectional view showing a radiofrequency module according to the second embodiment. The structure ofthe second embodiment is the same as that of the first embodiment exceptthat the multilayer substrate 3 is composed of five dielectric layersand six conductor layers and a cavity in which the SAW device 2 islocated extends from the dielectric layer 4 b to the dielectric layer 4e.

In this embodiment, a conductor pattern electrically connected with theconductor pattern 10 holding the power amplifier 1 is connected withanother conductor pattern electrically connected with the conductorpattern 13 holding the SAW device 2 at the conductor layers 5 e and 5 fwhich are located below the conductor pattern 13. Between the conductorlayers 5 a to 5 d, there is an area 300 in which the conductor pattern10 holding the power amplifier 1 and the other conductor patternelectrically connected with the conductor pattern 10 are not connectedwith the conductor pattern 13 holding the SAW device 2 and the otherconductor pattern electrically connected with the conductor pattern 13.

FIGS. 3A to 5B respectively show the respective conductor patterns onthe conductor layers 5 a to 5 f. The power amplifier 1 is mounted on theconductor pattern 10 as shown in FIG. 3A and the heat generated by thepower amplifier 1 is conducted through conductor patterns (shown in FIG.3A to FIG. 5B) horizontally or mainly through the via holes 11vertically. In this embodiment, the power amplifier is held by theconductor pattern 10 (as shown in FIG. 3A) while the SAW device 2 isheld by the conductor pattern 13 (as shown in FIG. 3B). The module isdesigned so that the conductor pattern 14 (FIG. 3B), conductor pattern15 (FIG. 4A) and conductor pattern 16 (FIG. 4B), which are electricallyconnected through the via holes 11 to the conductor pattern 10, are notconnected with the conductor pattern 31 (FIG. 4A) and conductor pattern32 (FIG. 4B) which are electrically connected through via holes 30 tothe conductor pattern 13 holding the SAW device, at the same layerlevel. On the other hand, as shown in FIGS. 5A and 5B, the conductorpattern electrically connected with the conductor pattern 10 and theconductor pattern electrically connected with the conductor pattern 13are connected with each other at the conductor layers 5 e and 5 f, by aconductor pattern 17 and a conductor pattern 18, respectively.

As a consequence, the heat generated by the power amplifier 1 is hardlyconducted to the conductor layer 5 b holding the SAW device 2 and theconductor layers located adjacent to it, 5 a, 5 c and 5 d, which curbsthe temperature rise of the conductor pattern 13 and enables the SAWdevice 2 to operate with stability.

The wiring which carries signals from the power amplifier 1 to the SAWdevice 2 crosses the boundary zone between the first area 100 to thesecond area 200 through a wiring pattern 60 provided on the conductorlayer 5 d as shown in FIG. 4B. The area of wiring which carries signalsfrom the power amplifier 1 to the SAW device 2 is smaller than that ofthe conductor patterns 10 and 14 and thus the amount of heat which isconducted from the first area 100 to the second are 200 is smaller.Accordingly, the influence of the heat conducted through the wiringpattern 60 on the SAW device 2 is not considerable so the wiring pattern60 need not always be provided on the conductor layer 5 d; instead itmay be provided on a layer above or below the conductor layer 5 d.

Therefore, even when the power amplifier 1 and SAW device 2 are mountedon the same multilayer substrate 3, the adoption of the structure asdefined by the present invention reduces the influence of the heatgenerated by the power amplifier 1 on the SAW device 2, so it ispossible to provide a radio frequency module which allows the SAW device2 to operate with stability even when both the devices are denselyintegrated in the substrate.

Next, a third embodiment of the present invention is described,referring to FIG. 6. FIG. 6 is a sectional view showing the thirdembodiment. The structure of the radio frequency module in the thirdembodiment is the same as that in the second embodiment except that viaholes 70 are provided between the conductor pattern 10 holding the poweramplifier 1 and the conductor pattern 13 holding the SAW device 2, inaddition to the via holes 11 located beneath the power amplifier 1.These via holes 70 further encourage the heat to be conductedvertically, thereby decreasing the amount of heat to be conductedtowards the conductor pattern 13 holding the SAW device 2. As aconsequence, the influence of the heat generated by the power amplifier1 on the SAW device 2 is reduced so it is possible to provide a radiofrequency module which allows the SAW device 2 to operate with stabilityeven when both the devices are densely integrated in the substrate.

Next, a fourth embodiment of the present invention is described,referring to FIG. 7. FIG. 7 is a sectional view showing the fourthembodiment. The structure of the radio frequency module in the fourthembodiment is the same as that in the second embodiment except thatthere is a groove 80 between the conductor pattern 10 holding the poweramplifier 1 and the conductor pattern 13 holding the SAW device 2. Thegroove 80 decreases the amount of heat to be conducted horizontally. Asa consequence, the influence of the heat generated by the poweramplifier 1 on the SAW device 2 is reduced so it is possible to providea radio frequency module which allows the SAW device 2 to operate withstability even when both the devices are densely integrated in thesubstrate.

Next, a fifth embodiment of the present invention is described,referring to FIG. 8. FIG. 8 is a sectional view showing the fifthembodiment. The structure of the radio frequency module in the fifthembodiment is the same as that in the second embodiment except that aconductor pattern 17 electrically connected with the conductor pattern10 holding the power amplifier 1 is electrically connected with a metallid 40 for the cavity 6 in which the SAW device 2 is located. Thedifference between the conductor layer 5 e in the second embodiment andthat in the fifth embodiment is explained below referring to FIG. 5E andFIG. 9.

FIG. 9 illustrates the conductor pattern on the conductor layer 5 e inthe radio frequency module according to the fifth embodiment while FIG.5E illustrates the conductor pattern on the conductor layer 5 eaccording to the second embodiment. In the second embodiment, an area 41which is in contact with the metal lid 40 for the cavity 6 is notelectrically connected with the conductor pattern 17 surrounding it. Onthe other hand, in the fifth embodiment, as shown in FIG. 9, theconductor pattern 17 is in contact with the area 41 which is in contactwith the metal lid 40. As a result, since the heat from the poweramplifier 1 is conducted to the metal lid 40, the heat is easier todisperse inside the radio frequency module than in the second embodimentand thus the overall temperature of the module is decreased, which leadsto a decrease in the temperature of the area in which the SAW device 2is located. Accordingly, the module structure according to thisembodiment makes the temperature rise of the conductor pattern 13holding the SAW device smaller than the module structure according tothe second embodiment. As a consequence, the adoption of the same modulestructure as defined by this embodiment reduces the influence of theheat generated by the power amplifier 1 on the SAW device 2 so it ispossible to provide a radio frequency module which allows the SAW device2 to operate with stability even when both the devices are denselyintegrated in the substrate.

Next, a sixth embodiment of the present invention is described,referring to FIG. 10. FIG. 10 is a sectional view showing the sixthembodiment. The structure of the module in this embodiment is the sameas that in the first embodiment except that the conductor pattern in thefirst area 100 and that in the second area 200 are not connected witheach other at the conductor layers 5 f and 5 g. Thus, the conductorpatterns which serve as the grounds in the first area 100 and the secondarea 200 are not connected at any layer, so horizontal heat conductionis smaller than in the first embodiment. This means that, although themodule temperature in the first area 199 may rise a little, the amountof heat which is conducted from the power amplifier 1 to the conductorpattern 13 holding the SAW device 2 can be reduced. Consequently it ispossible to provide a radio frequency module which allows the SAW device2 to operate with stability.

FIG. 11 shows a variation of the embodiment shown in FIG. 10. As can beseen from FIG. 11, in a situation that the radio frequency moduleaccording to the sixth embodiment of the present invention is mounted ona motherboard 350, a conductor-free zone 352 which fits the conductorfree area between the first area 100 and the second area 200 of theradio frequency module is made in a conductor pattern 351 on themotherboard 350 so that the heat which is conducted from the first area100 through the conductor on the motherboard 350 to the second area 200can be reduced. Hence, it is possible to provide a radio frequencymodule which allows the SAW device 2 to operate with stability even whenthe power amplifier 1 and the SAW device 2 are densely integrated in thesubstrate.

FIG. 12 shows a seventh embodiment of the present invention.

FIG. 13 shows an eighth embodiment of the present invention.

FIGS. 12 and 13 only show the shape of the multilayer substrate 3 andthe positional relationship between the power amplifier 1 and the SAWdevice 2 where the conductor patterns of the radio frequency module areomitted. Here, the conductor patterns on the respective layers are muchthe same as those in the embodiments mentioned earlier. In theseembodiments, the power amplifier 1 is located on the top face of themultilayer substrate 3 and the SAW device 2 is located inside the cavity6 made through the bottom of the substrate 3. The multilayer substrate 3is mounted on the motherboard 350.

In these embodiments, top view of the substrate of the radio frequencymodule is not rectangular but L-shaped or U-shaped and the poweramplifier 1 and the SAW device 2 are located in the peripheral area ofthe module as illustrated in FIGS. 12 and 13. The module structuresaccording to these embodiments make it possible to increase the distancebetween the power amplifier 1 and the SAW device 2 and thereby reduceheat conduction, resulting in a decrease in the temperature of the areain which the SAW device 2 is located. Part of the heat conducted to themotherboard 350 is conducted through themotherboard 350 by the conductorpattern 351. Therefore, as illustrated in FIG. 13, the conductor pattern351 on the motherboard 350 may have a conductor-free area 352 betweenthe SAW device 2 and the power amplifier 1.

Referring to FIG. 14, a ninth embodiment of the present invention isexplained next. The ninth embodiment is the same as the embodimentsmentioned so far except that the power amplifier 1 is located inside acavity 90 made in the multilayer substrate 3. Like the embodiment shownin FIG. 6, this embodiment has via holes 70 between the power amplifier1 and the SAW device 2 in addition to the via holes beneath the poweramplifier 1 in order to help the heat conduct towards the motherboard.

Referring to FIG. 15, a tenth embodiment of the present invention isexplained next. FIG. 15 shows a radio frequency module which combinesnot only the power amplifier 1 and the SAW device but also an RF-IC 400.In FIG. 15, the SAW device is located in a cavity (not shown). Thisembodiment has different areas with different functions: a first area100 which includes the power amplifier 1 and components of a matchingcircuit for the power amplifier; a second area 200 which includes filtercomponents such as a SAW device, switch, capacitance and inductor; and athird area 500 which includes an RF-IC 400 and components related toRF-IC operation.

In this case, although the conductors which serve as the grounds for therespective areas may be connected not within the multilayer substrate 3but on the motherboard 350 as in the embodiment shown in FIG. 10, fromthe viewpoint of suppressing the module temperature rise caused by theheat generated by the power amplifier 1 it is desirable to use astructure that conducts the heat throughout the module by connectingconductor patterns as far as possible while at the same time preventingthe heat from being conducted to the conductor pattern (not shown)holding the SAW device.

FIG. 16 is a sectional view taken along the dotted line A-B of FIG. 15.In the embodiment shown in FIG. 16, at the conductor layer holding theSAW device 2 and the conductor layers located above it, the conductorswhich serve as the grounds for the first area 100 and third area 500 arecontinuous with each other. In addition, via holes 71 and 72 areprovided under the RF-IC chip 400 and the SAW device respectively sothat the heat conducted to the third area 500 and the second area 200 isguided to the motherboard (not shown). As a consequence, the temperaturerise of the conductor pattern 13 holding the SAW device 2 is suppressedand thus it is possible to provide a radio frequency module whichenables the SAW device 2 to operate with stability.

FIG. 17 shows another example of a radio frequency module structure.Needless to say, the radio frequency module structure is not limited tothat shown in FIG. 16; it is acceptable to employ the radio frequencystructure as shown in FIG. 17 in which, while the conductor patternswhich serve as the grounds for the second area 200 and the third area500 are continuous with each other, the conductor patterns in the firstarea 100 are not connected at the conductor layer on which the conductorpattern 13 where the SAW device 2 is mounted and the conductor layerslocated above that layer.

This approach, in which the power amplifier and SAW device areintegrated in a module as described above, combined with a integrationof a switch and an RF-IC in the module, makes it easier to design radiofrequency circuit parts, requires a smaller number of man-hours forassembling, provides more handling ease and thus enables production ofterminals at lower cost than the conventional method in which componentsare individually assembled into a terminal.

As discussed so far, the adoption of a module structure according to thepresent invention makes it possible to provide a more compact radiofrequency module which assures more stable operation of a SAW devicewith no deterioration in the SAW device performance than existing radiofrequency modules.

It is apparent that the present invention is not limited to acombination of a power amplifier and a SAW device and may be applied toa combination of another type of heater element and another type ofdevice having sensitive temperature dependence of characteristics.

Furthermore, the invention may be embodied in any forms other than theabove-mentioned embodiments without departing from the spirit and scopeof the invention.

1. A radio frequency module comprising at least: a first chip forming aheater element on a first surface of a substrate; a second chip forming,on the second surface of the substrate, a device whose operatingcharacteristics vary with temperature change or whose maximum operatingtemperature is lower than the maximum operating temperature of the firstchip; and a multilayer substrate which is comprised of a plurality ofdielectric layers and a plurality of conductor layers and mechanicallysupports the first chip and the second chip with some of the conductorlayers electrically connected with these chips, wherein, the first chipis located on a first conductor pattern which serves as a groundingconductor for the first chip; the second chip is located on a secondconductor pattern which serves as a grounding conductor for the secondchip; and when the multilayer substrate is fixed on another substrate,it is fixed with its bottom face in contact with the other substrate andthe first conductor pattern and another conductor pattern electricallyconnected with the first conductor pattern are isolated from the secondconductor pattern and another conductor pattern electrically connectedwith the second conductor pattern at the conductor layer in which thesecond conductor pattern is formed and conductor layers closer to thetop face of the multilayer substrate than the conductor layer in whichthe second conductor pattern is formed.
 2. A radio frequency modulecomprising: a first chip; a second chip whose heat value per unit timeis smaller than that of the first chip; and a multilayer substratecomprised of a plurality of conductor layers and a plurality ofintermediate layers, where in the first chip and the second chip areelectrically connected with some of the conductor layers, and there area first structure for conducting the heat generated by the first chiphorizontally in the module and a second structure for conducting theheat vertically in the module, and wherein a heat isolation zone whichcrosses the line connecting the first chip and the second chip isspecified on a surface of the multilayer substrate and the areacorresponding to the projection from the heat isolation zone is removedin at least one of the conductor layers.
 3. A radio frequency modulecomprising: a first chip; a second chip whose heat value per unit timeis smaller than that of the first chip; and a multilayer substratecomprised of a plurality of conductor layers and a plurality ofintermediate layers, wherein the first chip and the second chip areelectrically connected with some of the conductor layers, and there area first structure for conducting the heat generated by the first chiphorizontally in the module and a second structure for conducting theheat vertically in the module, and wherein a heat isolation zone whichcrosses the line connecting the first chip and the second chip isspecified on a surface of the multilayer substrate and a groove is madein the area corresponding to the projection from the heat isolationzone.